Multilingual acquisition is a nonlinear and complex dynamic process. The past several decades of research have revealed that a number of factors interact and influence the variability of the process, including, for instance, the type of third language (L3) learner, learner proficiency, linguistic domain, grammatical feature, and language (psycho)typology (e.g., Cabrelli Amaro & Rothman, 2010; Llama, Cardoso, & Collins, 2010; Cenoz & Valencia, 1994; Gallardo del Puerto, 2007; Gibson, Hufeisen, & Libben, 2001; Pittman, 2008; Ringbom, 2001). Yet another crucial factor to consider, especially from the recent perspective of the Dynamic Model of Multilingualism (DMM) (Herdina & Jessner, 2002), is the linguistic background of the learner in relation to their literacy in the second language (L2), and more specifically, their metalinguistic knowledge and awareness (De Bot & Jaensch, 2013). The present brief discussion intends to call attention to the significant role of metalinguistic awareness in multilingual acquisition and offer critical suggestions for future research. First, a general review of relevant concepts is provided, centering upon the scope of research on multilingualism. Next, the roles and potential advantages of metalinguistic awareness in L3 acquisition is discussed, in comparison with those in first language (L1) and L2 acquisition. Finally and most importantly, several critical suggestions are provided for future research in the field of multilingualism.